Hormone Physiology Flashcards
1
Q
What is a hormone? What are the three types and what is each made from?
A
- a hormone is a substance that is secreted into the circulation and delivered to target tissues to elicit a particular response
- hormones are either peptides (from amino acids), steroids (from cholesterol), or amines (from tyrosine)
- (most hormones are peptide hormones)
2
Q
What are the major endocrine glands? What are the two other endocrine tissues?
A
- hypothalamus, pituitary (anterior and posterior), thyroid, parathyroids, adrenal glands (cortex and medulla), gonads, placenta, pancreas
- others: kidneys and the GIT
3
Q
What are the basic steps involved in peptide hormone synthesis?
A
- 1) normal gene transcription into mRNA
- 2) translation in ribosomes/E.R. to form the preprohormone
- 3) cleavage of signal peptide to form the pro hormone
- 4) prohomone gets packaged into secretory vesicles by the Golgi apparatus
- 5) cleavage of specific peptide sequences occurs within the vesicles to form the final peptide hormone
4
Q
Which endocrine glands synthesize steroid hormones? What are the main steroid hormones?
A
- (steroid hormones are made by modifying cholesterol)
- synthesized in adrenal cortex, gonads, corpus luteum, and placenta
- major steroid hormones: cortisol, aldosterone, estradiol, estriol, progesterone, testosterone, 1,25-dihydrocholecalciferol (vitamin D)
5
Q
What are the major amine hormones?
A
- (amine hormones are made by modifying tyrosine)
- catecholamines (epinephrine and norepinephrine) and thyroid hormones (T3/T4)
6
Q
What are the two general mechanisms of hormone synthesis regulation? Which is more common? Give an example of each.
A
- neural mechanisms and feedback mechanisms (much more common)
- neural: catecholamines are released at the ganglionic synapse via neural stimulation
- negative feedback: (nearly all hormones) cortisol inhibits ACTH secretion, thus leading to inhibition of cortisol secretion
- positive feedback (rare): oxytocin is secreted in response to cervical dilation and triggers uterine contractions to further cause cervical dilation, which triggers more oxytocin release (results in birth)
7
Q
What are the three major mechanisms by which hormones induce a response? What are the other two?
A
- major mechanisms: adenylyl cyclase mechanism, phospholipase C mechanism, steroid hormone mechanism
- others two: tyrosine kinase mechanism (for insulin) and guanylate cyclase mechanism
8
Q
What are GPCRs and what are their function? What are GRFs and GAFs?
A
- GPCRS are G-protein coupled receptors; they can be stimulatory (Gs), inhibitory (Gi), or Gq
- most hormone receptors are GPCRs
- they are heterotrimeric with an alpha, beta, and gamma subunit; the alpha subunit can bind GTP (activated) or GDP (inactivated), and has GTPase activity
- GRFs: guanosine releasing factors; these promote GDP dissociation from the Galpha subunit, promoting activation of the GPCR
- GAFs: GTPase activating factors; these promote GTP hydrolysis by the Galpha subunit, promoting inactivation of the GPCR
- when activated, the Galpha subunit will either stimulate or inhibit the associated effector protein
9
Q
Explain the adenylyl cyclase mechanism of hormone action.
A
- (this is one of three major mechanisms for hormone action; the other two are the phospholipase C and steroid hormone mechanisms)
- GPCR: Gi or Gs
- effector protein: adenylyl cyclase
- second messenger: cAMP
- activated protein: PKA
- when stimulated, adenylyl cyclase converts ATP into cAMP, which activates PKA
- PKA will go on to phosphorylate specific proteins that will execute the desired response/action
10
Q
Explain the phospholipase C mechanism of hormone action.
A
- (this is one of three major mechanisms for hormone action; the other two are the adenylyl cyclase and steroid hormone mechanisms)
- GPCR: Gq
- effector protein: phospholipase C
- second messenger: IP3 (inositol 1,4,5-triphosphate) and Ca2+
activated protein: PKC - phospholipase C converts PIP2 (phosphatidylinositol 4,5-diphosphate) into IP3 and DAG (diacylglycerol)
- the IP3 triggers Ca2+ release from the E.R. and/or S.R.
- together, DAG and Ca2+ activate PKC, which will go on to phosphorylate specific proteins that will execute the desired response/action
11
Q
Explain the steroid hormone mechanism of hormone action. What does this mechanism mean in terms of the triggered response when compared to the GPCR-related mechanisms?
A
- (this is one of three major mechanisms for hormone action; the other two are the adenylyl cyclase and phospholipase C mechanisms)
- this hormone diffuses into the target cell itself and binds to cytosolic or nuclear receptors, which initiate DNA transcription
- steroid hormones have multiple domains; the C domain is highly preserved and contains 2 Zn fingers that bind to DNA at specific SREs (steroid responsive elements), allowing the hormone to act as a TF
- because transcription and protein synthesis is involved, this means these steroid hormone responses are SLOWER than other hormone mechanisms
12
Q
What are the hormones of the hypothalamus? What is the general main function of each?
A
- TRH: stimulates secretion of TSH (and PRL) by AP
- CRH: stimulates secretion of ACTH by AP
- GnRH: stimulates secretion of LH and FSH by AP
- GHRH: stimulates secretion of GH by AP
- SRIF: inhibits secretion of GH
- PIF: inhibits secretion of PRL by AP (PIF is actually dopamine)
13
Q
What are the hormones of the anterior pituitary? What is the general main function of each?
A
- TSH: stimulates synthesis and secretion of T3/T4 by thyroid
- FSH: stimulates spermatogenesis in testes; stimulates follicular development and estrogen synthesis in ovaries
- LH: stimulates testosterone synthesis in testes; stimulates ovulation, formation of corpus luteum, estrogen and progesterone synthesis in ovaries
- GH: stimulates protein synthesis, IGF-1 synthesis in liver, and overall growth
- PRL: stimulates breast milk production and assists in its secretion
- ACTH: stimulates synthesis and secretion of adrenocortical hormones (aldosterone, cortisol, androgens)
- (MSH: stimulates melanin synthesis in melanocytes)
14
Q
What are the hormones of the posterior pituitary? What is the general main function of each?
A
- ADH/vasopressin: stimulates water reabsorption in kidneys and arterial vasoconstriction
- oxytocin: stimulates milk ejection from breasts, stimulates uterine contractions
15
Q
What are the hormones of the thyroid? What is the general main function of each?
A
- T3 and T4: stimulates skeletal growth; oxygen consumption (basal metabolic rate); heat production; protein, fat, and carbohydrate utilization; brain development
- (the “4 B’s”: brain maturation, bone growth, Beta-1 adrenergic effects, and basal metabolic rate)
- calcitonin: decreases serum Ca2+
